Sorted CD69lo wt DP thymocytes and mature (TCRhi or Vα2hi CD24lo) CD4 SP thymocytes from Wt, Jmjd3KO, UtxKO and dKO mice were digested with MNase, followed by sonication to generate mononucleosomes. Sonicated supernatants were pre-cleared with protein G beads and then immunoprecipitated with anti-H3K27Me3. The libraries were prepared according to standard Illumina's protocol. The ChIP DNA is blunt-ended and phosphorylated. A single 'A' nucleotide is added to the 3' ends of the fragments in preparation for ligation to an adapter that has a single-base 'T' overhang. The ligation products are purified and size-selected. The size-selected DNA is purified and PCR-amplified to enrich for fragments that have adapters on both ends. The final purified product is then quantitated by qPCR before cluster generation and sequencing. Clusters were generated on an Illumina flow cell and libraries were sequenced on the Genome Analyzer following the manufacturer's protocols.